[LU-9723] test large xattr (ea_inode) patch interoperability

Related — Fri, 10 Aug 2018 03:11:00 +0000

The large xattr (ea_inode) feature patches are being merged into the upstream 4.13 kernel, but additional changes are being built on top of the EA inode functionality that we use in the ldiskfs patch series. In particular, in the upstream patch series the EA inodes can be shared among multiple parent inodes, and instead of having a backpointer to the parent inode/generation the shared inodes have a refcount and a hash of the xattr value to verify that the correct xattr is referenced. Once we update to a newer vendor kernel that includes these changes, we can remove the patch from ldiskfs to reduce ongoing maintenance efforts, but we can't wait until that time to verify that the feature works properly with existing Lustre filesystems.

There is supposed to be interoperability functionality in the upstream feature to allow access to existing Lustre EA inodes. We need to test that the ext4 patches being landed to the upstream kernel are able to work with xattrs created by Lustre, and that the upstream e2fsprogs will not consider Lustre EA inodes to be corrupt. This testing needs to be done in the next week or two, to ensure that we can feed back any issues to the upstream ext4 maintainers before that feature is released in an upstream kernel.

For testing, something like the following process should be sufficient:

create an MDT filesystem with an existing RHEL7 kernel with --mkfsoptions="-O ea_inode"
mount filesystem as type lustre
create large user.test xattrs via setfattr (up to 64KiB) with verifiable data (e.g. filename repeated many times)
dump all xattrs via getfattr -d -m user.test testfiles > xattrs.lustre
upgrade the kernel to upstream kernel
disable the dirdata feature via debugfs -w -R "feature ^dirdata" /dev/MDT and mount it as type ext4
dump all xattrs via getfattr -d -m user.test testfiles > xattrs.ext4 and compare to xattrs.lustre to verify xattr consistency and ensure that no errors are generated by the kernel
run new e2fsck on updated filesystem to verify that it does not consider the EA inodes as corrupted, at worst it should offer to fix the refcount and hash values of those inodes

The upstream kernel patches are included on the dev branch of https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git (all of the patches from author "Tahsin Erdogan") but could potentially also be pushed as a series to the fs/linux-staging branch (with Test-Parameters: forbuildonly since there is no benefit to Lustre testing on them) in order to have Jenkins build the patches for testing via loadjenkinsbuild.

Whamcloud Community JIRA

[LU-9723] test large xattr (ea_inode) patch interoperability